1. Field of the Invention
The present invention relates to a connection structure for connecting dielectric waveguide lines principally for use in transmitting high-frequency signals in the microwave or millimeter wave band.
2. Description of the Related Art
In recent years, research in mobile communications, inter-vehicular radars or the like in which high-frequency signals within the microwave or millimeter wave band are used, been increasingly carried out. As a transmission line for transmitting such high-frequency signals, coaxial lines, waveguide lines, dielectric waveguide lines, microstrip lines and the like are known.
Moreover, there has recently been proposed a dielectric waveguide line that is formed in a wiring substrate composed of laminated multiple dielectric layers. For example, Japanese Unexamined Patent Publication JP-A 6-53711(1994) proposes a waveguide line which is formed by sandwiching a dielectric substrate between a pair of main conductor layers and forming side walls of two rows of via-holes which connect the main conductor layers to each other. Namely, in this waveguide line, the dielectric material is surrounded by the pair of main conductor layers and the via-holes as pseudo conductor walls thereby to use the region inside these conductor walls as a dielectric line for signal transmission.
Further, the inventors of the present invention proposed in Japanese Unexamined Patent Publication JP-A 10-75108 (1998) a dielectric waveguide line of a multilayer structure which is formed within a dielectric substrate. This is also referred to as a lamination type waveguide, in which a dielectric waveguide line as described above is composed of a dielectric layer, a pair of main conductor layers and through conductor groups such as via-hole groups, and in addition to the through conductor groups sub conductor layers are further provided to reinforce the side walls which serve as electrical walls. In the dielectric waveguide line as disclosed in JP-A 6-53711, if an electric field not parallel to the via-holes is generated within the waveguide, the electric field will leak through the side walls. According to the lamination type waveguide, however, the electric field will not leak owing to the sub conductor layers.
Such a dielectric waveguide line which can be disposed inside the wiring substrate or the like is originally intended for use as a transmission line in a multilayer wiring substrate mainly for microwaves and millimeter waves or in a package for housing a semiconductor device, and it can also be used as a feed line for an antenna which is integrated into the multilayer wiring substrate or the package for housing a semiconductor device to provide a sophisticated function.
In general, in the case of using transmission lines to constitute a high-frequency circuit, and in particular, in the case of forming a feed line for an array antenna or the like, it is necessary to connect the transmission lines to each other in a wiring circuit within the transmission lines or disposed on a branch circuit.
Such dielectric waveguide line may be stacked one over another, however, if downsizing and high integration is desired, it is necessary to connect the dielectric waveguide lines to each other. In the case of the conventional metallic waveguides, there is no need for a specific connection technique because three-dimensional connection can be done by simply bending the metallic waveguides.
With regard to the connection of the dielectric waveguide lines stacked one over another, the inventors of the present invention have already proposed a connection structure with feed pins formed by via-holes. This connection structure enables the connection between the dielectric waveguide lines which are stacked one over another within a dielectric substrate.
However, even in this connection structure, there still remain problems to be solved as follows.
For example, in the above connection structure, the feed pin functions as a mono-pole antenna of xc2xc wavelength within the dielectric waveguide line. Accordingly, it is necessary to adjust the length of the feed pin to a quarter of the wavelength of a signal most desired to be transmitted. However, since the feed pin is formed by a through conductor such as a via-hole, the length thereof is restricted to the thickness of dielectric sheets which are laminated to form the dielectric substrate in which the dielectric waveguide line is formed. Of course the thickness of the dielectric sheets may be changed so that the feed pin is set to a desired length, which, however, causes a problem that adaptability to various designs is impaired, and consequently results in an increase in cost.
Further, electric current flows concentratedly in the feed pin, in particular, in the millimeter wave band, the electric current concentrates on the surface of the feed pin under the influence of skin effect, with the result that an energy loss due to the conductor resistance is large.
Furthermore, although the dielectric waveguide line may be used in a mode where the lamination plane of laminated dielectric sheets is parallel with the E plane of the waveguide, i.e., in a mode where the electric field is parallel to the lamination plane, in this case excitation of electric current will not occur in the feed pin making it impossible to connect the dielectric waveguide lines together when they are stacked one over another.
In addition, in the case of simply disposing a branch to a dielectric waveguide line for signal transmission surrounded by artificial conductor walls formed by the pair of conductor layers and the two rows of via holes, as proposed in JP-A 6-53711, the electromagnetic field is disturbed and large transmission loss occurs.
Therefore, in order to constitute a high-frequency circuit by producing a transmission line circuit provided with a branch for forming a feed line for an array antenna or the like within a dielectric substrate, such a branch structure for dielectric waveguide lines is desired that can be formed within a dielectric substrate, prevent radiation of electromagnetic waves and have minimal transmission loss.
The invention was made to solve the above-mentioned problems, and it is an object of the invention to provide a connection structure for dielectric waveguide lines which can be readily manufactured by the conventional multi-layering technique, the connection structure being capable of giving freedom of design and enabling easy connection of dielectric waveguide lines stacked one over another within a dielectric substrate.
It is another object of the invention to provide a connection structure for dielectric waveguide lines which can be readily manufactured by the conventional multi-layering technique, the connection structure being capable of easily connecting the dielectric waveguide lines which are stacked one over the other within a dielectric substrate so as to be orthogonal to each other.
It is still another object of the invention to provide a connection structure for dielectric waveguide lines in which dielectric waveguide lines can be formed within a dielectric substrate without radiation and leakage of electromagnetic waves of high-frequency signals, wherein the circuit can branch into a shape of T or a right-angled three-forked line, having little transmission loss and excellent transmission characteristics which is achieved by connecting one dielectric waveguide line to another one so as to intersect each other.
The inventors of the invention have made efforts for solving the above-mentioned problems and found that by stacking two dielectric waveguide lines formed within a dielectric substrate, one over the other so that a part of an upper main conductor layer of the dielectric waveguide line formed at the lower side and a part of a lower main conductor layer of the dielectric waveguide line formed at the upper side overlap each other, and providing a coupling window in the overlap part of the main conductors, the upper and lower dielectric waveguide lines can be electromagnetically coupled.
The invention provides a connection structure for dielectric waveguide lines, comprising two dielectric waveguide lines each including a dielectric substrate; a pair of main conductor layers, the dielectric substrate being sandwiched between the pair of main conductor layers; two rows of side-wall through conductor groups arranged in a transmission direction of high-frequency signals at intervals less than one half of a signal wavelength so as to electrically connect the main conductor layers; and a sub conductor layer disposed between the main conductor layers so as to be parallel with the main conductor layers, the sub conductor layer being electrically connected with the side-wall through conductor groups, the dielectric waveguide lines thereby transmitting high-frequency signals through a region surrounded by the main conductor layers, the side-wall through conductor groups and the sub conductor layer, wherein the two dielectric waveguide lines are stacked one over the other so that one of the main conductor layers of one dielectric waveguide line and one of the main conductor layers of the other dielectric waveguide line overlap each other to define an overlap part, in which a coupling window is formed.
In the invention, it is preferable that the dielectric waveguide line further includes an end through conductor group provided at a distance equal to or less than a guide wavelength of the high-frequency signals from a center which is a central position of a length of the coupling window in the transmission direction, in the transmission direction (dxe2x89xa6xcex), which end through conductor group is arranged at intervals less than one half of the signal wavelength in a direction orthogonal to the transmission direction (P1 less than xcex/2) so as to electrically connect the main conductor layers, and an end sub conductor layer disposed between the main conductor layers so as to be parallel with the main conductor layers, and electrically connected to the sub conductor layer and the end through conductor group.
In the invention, it is preferable that the end through conductor group and end sub conductor layer are formed at a distance from an end of the coupling window in the transmission direction.
In the invention, it is preferable that the end through conductor group and end sub conductor layer are disposed at positions which are substantially in an end portion of the coupling window in the transmission direction.
As detailed above, according to the connection structure for dielectric waveguide lines of the invention, in the connection portion between the lower dielectric waveguide line and the upper dielectric waveguide line which are stacked one over the other within the dielectric substrate, the lower main conductor layer of the upper dielectric waveguide line and the upper main conductor layer of the lower dielectric waveguide line overlap each other so as to be used in common, and a portion which lacks for a main conductor layer is provided as a coupling window in the overlap part. As a result, the thickness of dielectric sheets constitutes no restriction on characteristics of the resulting waveguide line in contrast to the conventional connection structure via a feed pin. For example, since the pattern of the coupling window can be previously made when the overlap part of the main conductor layers of two dielectric waveguide lines is printed before lamination of green sheets, formation of the coupling window is facilitated and a connection structure of good productivity is realized with low production costs.
Further, in the case of forming the coupling window in the connection structure for dielectric waveguide lines of the invention, the position, profile and size of the coupling window are complicatedly related to the frequency characteristics, coupling amount and reflection amount which are required for the connection structure, and the connection structure of the invention has enhanced freedom of design as compared with the conventional method using a feed pin to facilitate circuit design.
Furthermore, since concentration of electric current on the surface of the feed pin as observed in the connection structure using the feed pin does not occur, an energy loss due to the connection between dielectric waveguide lines is small.
As mentioned above, the invention makes it possible to provide a connection structure for dielectric waveguide lines which can be easily fabricated by the conventional multi-layering technique, which connection structure offers freedom of circuit design and makes it possible to readily connect the dielectric waveguide lines stacked one over another.
Next, the inventors of the invention have found that by stacking two dielectric waveguide lines one over the other within a dielectric substrate so that the dielectric waveguide lines are orthogonal to each other and so that a part of an upper main conductor layer of the dielectric waveguide line formed at the lower side and a part of a lower main conductor layer of the dielectric line formed at the upper side overlap each other so as to be used in common, and by providing a coupling window for high-frequency signals in the partial main conductor used in common as a clear portion which lacks for a main conductor, the upper and lower dielectric waveguide lines can be electromagnetically coupled.
According to this connection structure, high-frequency signals inputted from one dielectric waveguide line can propagate through the coupling window into the other dielectric waveguide line on the output side which is orthogonal to the one dielectric waveguide line, in two directions in the same phase. The coupling window which lacks a conductor, disposed between two waveguide lines, is identical to a hole called a Bethe-hole in the conventional waveguide line and utilized for a branch structure or directional coupler.
Further, the inventors have also found that by increasing the width or decreasing the thickness of the two dielectric waveguide lines in the connection portion thereof, it is made possible to use the portion as a matching portion for impedance matching to reduce reflection of high-frequency signals due to noncontinuity of impedance.
The invention provides a connection structure for dielectric waveguide lines comprising two dielectric waveguide lines each including a dielectric substrate, a pair of main conductor layers, the dielectric substrate being sandwiched between the pair of main conductor layers, two rows of side-wall through conductor groups arranged in a transmission direction of high-frequency signals at repetition intervals less than one half of a signal wavelength in a transmission direction of high-frequency signals and in a direction orthogonal to the transmission direction at a predetermined width, so as to electrically connect the main conductor layers, and a sub conductor layer disposed between the main conductor layers so as to be parallel with the main conductor layers, the sub conductor layer being electrically connected with the side-wall through conductor groups, the two dielectric waveguide lines thereby transmitting high-frequency signals through a region surrounded by the main conductor layers, the side-wall through conductor groups and the sub conductor layer, wherein the two said dielectric waveguide lines are stacked one over the other so that the transmission directions of high-frequency signals thereof are orthogonal to each other and one of the main conductor layers of one dielectric waveguide line and one of the main conductor layers of the other dielectric waveguide line overlap each other, and a coupling window is formed in the overlap part of the main conductor layers.
Further, in the invention it is preferable that the dielectric waveguide line further includes an end through conductor group, provided at a distance equal to or less than a guide wavelength of the high-frequency signals from a center of the coupling window to the transmission direction of the dielectric waveguide line, which end through conductor group is arranged at intervals less than one half of the signal wavelength in a direction orthogonal to the transmission direction so as to electrically connect the main conductor layers, and an end sub conductor layer is disposed between the main conductor layers so as to be parallel with the main conductor layers, and to be electrically connected to the sub conductor layer and the end through conductor group.
Furthermore, in the invention it is preferable that a width of the two rows of side-wall through conductor groups of the dielectric waveguide lines in the overlap part of the dielectric waveguide lines is larger than the predetermined width.
In addition, in the invention it is preferable that an interval between the pair of main conductor layers of the dielectric waveguide lines in the overlap part of the dielectric waveguide lines is narrower than an interval therebetween in the remaining part.
According to the connection structure for dielectric waveguide lines of the invention, the first and second dielectric waveguide lines overlap each other so as to be orthogonal to each other, and a coupling window is disposed as a portion which lacks a conductor, in the main conductor layers in the overlap part, whereby the two dielectric waveguide lines are coupled by an electromagnetic field, and high-frequency signals inputted from one of the dielectric waveguide lines also propagate into the other dielectric waveguide line via the coupling window. Since there are two directions to propagate in the other dielectric waveguide line, the high-frequency signals propagate in the two directions, thereby branching into three directions including the two directions and the transmission direction in the first dielectric waveguide line.
Further, according to the connection structure for dielectric waveguide lines of the invention, in the above configuration, the end face through conductor groups and the end sub conductor layers are provided at a predetermined distance from the center of the coupling window, and hence when the end face through conductor groups and the end sub conductor layers are provided in one of the dielectric waveguide lines, it is possible to branch the propagation of high-frequency signals in a T-shaped configuration. When the end face through conductor groups and the end sub conductor layers are provided in both the dielectric waveguide lines, it is possible to cause high-frequency signals to propagate in an L-shaped configuration.
Furthermore, according to the connection structure for dielectric waveguide lines of the invention, in the above configuration, by increasing the width of at least one of the dielectric waveguide lines in the overlap part of the dielectric waveguide lines, i.e., the width between the side-wall through conductor groups in a direction orthogonal to the transmission direction, or decreasing the thickness of at least one of the dielectric waveguide lines in the overlap part of the dielectric waveguide lines, i.e., the distance between the pair of main conductor layers, it is possible to reduce the discontinuity of impedance of the dielectric waveguide lines at the connection portion to realize connection with little reflection of high-frequency signals and small transmission loss. Thus increasing the width or decreasing the thickness may be made for both the dielectric waveguide lines and the combination thereof may be made.
As described above, according to the connection structure for dielectric waveguide lines of the invention, in any of the configurations, it is possible to reduce a mismatch of the characteristic impedance of the dielectric waveguide lines before and after the connection portion to thereby decrease reflection of high-frequency signals at the connection portion, and moreover to prohibit disturbance of a propagation mode at the connection portion, with the result that such a connection structure for dielectric waveguide lines can be obtained that shows little transmission loss and has excellent transmission characteristic.
In other words, according to the connection structure for dielectric waveguide lines of the invention, at the connection portion of the lower dielectric waveguide line and the upper dielectric waveguide line which are stacked one over the other so that the transmission directions are orthogonal to each other within a dielectric substrate, one of the main conductor layers, i.e., the upper main conductor layer of the lower dielectric waveguide line and the lower main conductor layer of the upper waveguide line overlap each other, and a coupling window is disposed in the overlap part of the main conductor layers, whereby the two dielectric waveguide lines are coupled by an electromagnetic field, and high-frequency signals inputted from one of the dielectric waveguide lines also propagate into the other dielectric waveguide line via the coupling window. Since there are two directions of propagation of signals in the other dielectric waveguide line, the high-frequency signals propagate in the two directions, whereby propagation of signals is branched into three directions including the two directions and the transmission direction in the first dielectric waveguide line.
Further, according to the connection structure for dielectric waveguide lines of the invention, in the above configuration, the end face through conductor groups and the end sub conductor layers are provided at a predetermined distance from the center of the coupling window, so that when they are provided in one of the dielectric waveguide lines, it is possible to branch the propagation of high-frequency signals in a T-shaped configuration and when the end face through conductor groups and the end sub conductor layers are provided in both the dielectric waveguide lines, it is possible to make high-frequency signals propagate in an L-shaped configuration.
Furthermore, according to the connection structure for dielectric waveguide lines of the invention, in the above configuration, by increasing the width of at least one of the dielectric waveguide lines in the overlap part of the dielectric waveguide lines, i.e., the width between the side-wall through conductor groups in a direction orthogonal to the transmission direction, or decreasing the thickness of at least one of the dielectric waveguide lines in the overlap part of the dielectric waveguide lines, i.e., the distance between the pair of main conductor layers, it is possible to reduce the discontinuity of impedance of the dielectric waveguide lines at the connection portion to realize connection with little reflection of high-frequency signals and small transmission loss.
As shown above, according to the invention, it is possible to provide a connection structure for dielectric waveguide lines which can be readily manufactured by the conventional multi-layering technique, the connection structure being capable of easily connecting the dielectric waveguide lines stacked one over the other so as to be orthogonal to each other within a dielectric substrate.
Further, according to the invention, it is possible to provide such a connection structure for dielectric waveguide lines that can be formed in a dielectric substrate without radiation and leakage of electromagnetic waves of high-frequency signals, the connection structure capable of connecting two dielectric waveguide lines so as to be branched into a shape of T or into three lines intersecting at right angles with a little transmission loss and good transmission characteristics.